<template>
<div>
  <router-link tag="div" to="/" class="header-abs" v-show="showAbs">
    <div class="iconfont header-abs-back">&#xe624;</div>
  </router-link>
  <div class="header-fixed" v-show="!showAbs" :style="opactiyStyle">
    <router-link to="/">
      <div class="header-left"><div class="iconfont header-fixed-back">&#xe624;</div></div>
    </router-link>
    景点详情
  </div>
</div>
</template>

<script>
export default {
  name: 'DetailHeader',
  data () {
    return {
      showAbs: true,
      opactiyStyle: {
        opacity: 0
      }
    }
  },
  // 因为用了keepalive，所以要用activated；当取消缓存时，要用回mounted
  mounted () {
    // 页面展示的时候去绑定 scroll 事件，
    window.addEventListener('scroll', this.handleScroll)
  },
  // 页面即将被隐藏 或者说 页面即将被替换成新的页面时，deactivated会被执行
  deactivated () {
    // 而页面被隐藏的时候，再去对 scroll 这个全局事件进行一个解绑。
    window.removeEventListener('scroll', this.handleScroll)
  },
  methods: {
    handleScroll () {
      // console.log(document.documentElement.scrollTop)
      const top = document.documentElement.scrollTop
      if (top > 60) {
        let opacity = top / 140
        opacity = opacity > 1 ? 1 : opacity
        this.opactiyStyle = {
          opacity: opacity
        }
        this.showAbs = false
      } else {
        this.showAbs = true
      }
    }
  }
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.header-abs
  position: absolute
  left: .2rem
  top: .2rem
  width: .8rem
  height: .8rem
  line-height: .8rem
  text-align:center
  border-radius: .4rem
  background: rgba(0, 0, 0, .8)
  .header-abs-back
    color: #fff
    font-size: .4rem
.header-fixed
  z-index: 2
  position: fixed
  top: 0
  left: 0
  right: 0
  height $headerHeight
  line-height $headerHeight
  text-align:center
  color:#fff
  font-size: .32rem
  background: $bgColor
  .header-fixed-back
    position:absolute
    top:0
    left:0
    width: .64rem
    text-align: center
    font-size: .4rem
    color: #fff
</style>
